Polystyrene foam materials are well known in the art. A summary of polystyrene and related thermoplastic foams is disclosed by Ingram et al. In Plastic Foams, Part II, Chapter 10, edited by Frisch et al., Marcel Dekker, Inc., New York (1973). Extruded low-density foam articles comprising a mixture of polystyrene and polyphenylene oxide are also known in the art as demonstrated by the Allen et al. U.S. Pat. No. 4,857,390, the Krutchen et al. U.S. Pat. Nos. 4,535,100, 4,598,100 and 4,532,263, and German Reference No. DE 3220856. The Park U.S. Pat. Nos. 4,661,302, 4,705,811 and 4,734,441 additionally disclose the use of polyphenylene oxide to enhance the melt strength of expanded polystyrene foam board during post expansion processes.
Polystyrene materials are used in numerous industrial and consumer applications. In view of the great amount of polystyrene materials appearing in waste refuse, it is desirable to recycle post-use polystyrene materials for reuse. One type of polystyrene material which has been successfully recycled for reuse comprises polystyrene foam and solid materials which have been employed in food packaging, for example, in fast food restaurants. In one process, the used polystyrene material is sorted by hand, washed, devolatized, ground and extruded into pellets to provide a recycled material having a melt flow index of between 3 and 4 g/10 min (ASTM D-1238, Condition G). The recycled material has been used to produce injection molded non-food contact products.
However, one type of polystyrene material which has not been successfully recycled for further use comprises bromine-modified polystyrene foams. The bromine-modified polystyrene foam materials are commonly used in industrial packaging applications, for example, consumer electronics and appliances, and comprise about 60% of all polystyrene waste refuse. The bromine modifiers are, for example, compounds containing aliphatic, cycloaliphatic and aromatic bromine, and are originally included in the polystyrene foams in order to improve their processability and to serve as flame retardants for the foam materials. However, the bromine-containing compounds have relatively low thermal stability. Thus, when the bromine-modified polystyrene foam materials are heated, the bromine-containing modifiers thermally decompose. The decomposition products react with the polystyrene to cause large reductions of molecular weight, resulting in a nonusable product. Heating of the bromine-modified polystyrene foams above their glass transition temperatures causes devolatization of the foam materials and provides products having a melt flow index greater than about 25, and oftentimes having a melt flow index greater than about 100. In view of the high melt flow index of this material, such products were heretofore believed unsuitable for further practical use.
Thus, a need exists for further advances in the development and use of post-consumer polystyrene materials.